1. Field of the Invention
The present invention relates to a fundus camera used for photographing a fundus of a subject's eye in an ophthalmologist's office or the like.
2. Description of the Related Art
Hitherto, a fundus camera has been known, which includes a projecting unit for projecting a focus split target light flux being split on the pupil of a subject's eye onto the fundus thereof and an observing/photographing unit, provided with a focusing lens, for observing and photographing the fundus thereof. Both of the units are interlockingly moved in the direction of an optical axis. An operator can easily adjust the focus of the fundus camera by observing focus split target images formed on the fundus of the subject's eye and bringing the focus split target images into a predetermined positional relationship, i.e., aligning the focus split target images in a line. In addition, a device has been known, which achieves autofocus by capturing focus split target images and detecting the positions of the focus split target images.
Techniques for facilitating focusing a fundus camera on the fundus of a subject's eye have been known, which project a focus split target being split on the pupil of a subject's eye onto the fundus and observe images of the projected focus split target via a focusing lens of a fundus observing/photographing optical system, and which perform focusing by observing a positional relationship of the focus split target images.
In addition, techniques for achieving autofocus have been known, which perform imaging of focus split target images projected onto a subject's eye fundus and which perform focusing by observing a positional relationship of the focus split target images.
Japanese Patent Application Laid-Open No. 5-95907 discusses a fundus camera that performs imaging of two focus split images projected onto a subject's eye fundus and detects a focus state based on positions of the two focus split target images while attenuating the brightness of the target.
Japanese Patent Application Laid-Open No. 8-275921 discusses an ophthalmologic apparatus that projects a focus target onto the fundus of a subject's eye and performs imaging of focus target images using a photographing optical system, thereby detecting a focus state.
However, in order to eliminate reflection light from a subject's eye cornea, conventional fundus cameras are constructed such that a fundus illumination light flux or a focus split target light flux and an observing/photographing light flux are respectively incident upon different areas in the vicinity of a subject's eye pupil. Accordingly, in a case where an aberration of an optical system of a subject's eye varies among individuals, when a subject's eye fundus is photographed only by setting the positions of the focus split target images in a predetermined positional relationship, a focusing error may be caused in some subject's eye. Consequently, a fundus image may be out of focus.